Dual auger mixing system

ABSTRACT

A mixing system for an exhaust aftertreatment system includes a first mixing device having a plurality of first auger blades and an inlet having a first cross-sectional area. A second mixing device is separate and downstream from the first mixing device and includes a second auger blade. The second mixing device includes an inlet having a second cross-sectional area greater than the first cross-sectional area. A plurality of flow paths created by the first mixing device are recombined into a single flow path between the first and second mixing devices. A longitudinal center line of the first mixing device is offset from a longitudinal center line of the second mixing device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/119,923, filed on Feb. 24, 2015. The entire disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to a dual auger mixing system for anexhaust aftertreatment system.

BACKGROUND

This section provides background information related to the presentdisclosure and is not necessarily prior art.

Selective catalytic reduction technology has been used in conjunctionwith reducing nitrogen oxides present in the exhaust of combustionengines. Many vehicles utilizing combustion engines are equipped withexhaust aftertreatment devices for reducing nitrogen oxide emissions.Some of these systems include a reductant delivery system fortransmitting the reductant (e.g., urea) from a tank to the exhauststream. A mixer may be provided for mixing the injected reductant withthe exhaust gas before the reductant reaches a catalyst with which thereductant reacts. While these systems may have performed well in thepast, it may be desirable to provide an improved mixing system that isable to fit in a limited packaging space and can more efficientlydecompose and atomize the reductant and mix the reductant with theexhaust stream.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one form, the present disclosure provides a mixing system for anexhaust aftertreatment system. The mixing system may include first andsecond mixing devices. The first mixing device may include a pluralityof first auger blades attached to a central shaft and defining aplurality of flow paths through the first mixing device. Each of thefirst auger blades may be axially aligned with each other and angularlyspaced apart from each other. The second mixing device may be separateand distinct from the first mixing device and may be disposed downstreamof the first mixing device. The second mixing device may include asecond auger blade. The plurality of flow paths created by the firstmixing device may recombine into a single flow path between the firstand second mixing devices.

In another form, the present disclosure provides a mixing system for anexhaust aftertreatment system. The mixing system is disposed within anexhaust pipe and may include first and second mixing devices and abaffle plate. The first mixing device may include a plurality of firstauger blades defining a plurality of flow paths through the first mixingdevice. The second mixing device may be separate and distinct from thefirst mixing device and may be disposed downstream of the first mixingdevice. The second mixing device may include a second auger blade. Theplurality of flow paths created by the first mixing device may recombineinto a single flow path between the first and second mixing devices. Thebaffle plate may be separate and distinct from the second mixing deviceand may be disposed downstream of the second mixing device.

In another form, the present disclosure provides a mixing system for anexhaust aftertreatment system including a first mixing device having aplurality of first auger blades and an inlet having a firstcross-sectional area. A second mixing device is separate and downstreamfrom the first mixing device and includes a second auger blade. Thesecond mixing device includes an inlet having a second cross-sectionalarea greater than the first cross-sectional area. A plurality of flowpaths created by the first mixing device are recombined into a singleflow path between the first and second mixing devices. A longitudinalcenter line of the first mixing device is offset from a longitudinalcenter line of the second mixing device.

In some configurations, the baffle plate includes a plurality of firstapertures, a plurality of second apertures and a plurality of thirdapertures. The first apertures may be disposed proximate a periphery ofthe baffle plate and are each smaller than the second and thirdapertures. The second apertures may be disposed radially between thefirst apertures and the third apertures and are each smaller than thethird apertures. The third apertures may be arranged proximate a centerof the baffle plate.

In some configurations, the first mixing device includes a taperedcentral shaft about which the first auger blades extend.

In some configurations, the second mixing device includes a centralshaft about which the second auger blade extends. The central shaft mayinclude an aperture extending axially therethrough.

In some configurations, each of the first auger blades includes aplurality of apertures.

In some configurations, each of the first auger blades extends 180degrees around a central shaft.

In some configurations, the first auger blades extend in the samerotational direction around the central shaft.

In some configurations, the second auger blade include a plurality ofapertures.

In some configurations, the second auger blade extends 360 degreesaround a central shaft.

In some configurations, the second auger blade extends between 180degrees and 720 degrees around a second central shaft.

In some configurations, the second mixing device includes only a singleauger blade.

In some configurations, the first mixing device is disposed within afirst portion of the exhaust pipe, and the second mixing device and thebaffle plate are disposed in a second portion of the exhaust pipe. Thesecond portion may have a larger diameter than the first portion.

In some configurations, a longitudinal centerline of the first portionis offset from a longitudinal centerline of the second portion.

In another form, the present disclosure provides an exhaustaftertreatment system including the mixing system, a reductant injectordisposed upstream of the first mixing device, and a catalyst disposeddownstream of the baffle plate.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic representation of an exhaust aftertreatment systemhaving a mixing system according to the principles of the presentdisclosure;

FIG. 2 is a perspective view of a portion of an exhaust pipe with themixing system of FIG. 1 disposed therein;

FIG. 3 is a perspective view of a first mixing device of the mixingsystem;

FIG. 4 is a side view of the first mixing device;

FIG. 5 is an end view of the first mixing device;

FIG. 6 is a side view of a second mixing device of the mixing system;

FIG. 7 is a perspective view of the second mixing device;

FIG. 8 is an end view of the second mixing device;

FIG. 9 is an end view of a baffle plate of the mixing system;

FIG. 10 is a perspective view of a portion of an alternate mixingsystem; and

FIG. 11 is a schematic of a portion of an alternate mixing system.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

With reference to FIG. 1, an exhaust aftertreatment system 10 isprovided that may include an exhaust pipe 12, a reductant deliverysystem 14, a mixing system 16 and an aftertreatment device 17 disposeddownstream of the mixing system 16. The exhaust pipe 12 may receiveexhaust gas discharged from a combustion engine 11. Exhaust gas may flowthrough the exhaust pipe 12, the mixing system 16 and the aftertreatmentdevice 17 before being discharged to the ambient environment. Theaftertreatment device 17 can include a selective catalytic reduction(SCR) catalyst or an SCR coated diesel particulate filter (DPF), forexample. The reductant delivery system 14 can include a reductant tank18 and an injector 19 (shown schematically in FIGS. 1 and 2) configuredto inject a reductant (e.g., urea) into the exhaust pipe 12 upstream ofthe mixing system 16. The mixing system 16 performs decomposition andatomization within the exhaust stream within a reduced axial pathway andincreases particle residency in the exhaust stream by inducing radialflow components in the exhaust stream that oppose the natural axialexhaust flow path through the exhaust pipe 12. The mixing system 16creates a series of axial flows, radial flows, micro flows, macro flowsand combinations thereof to transmute system energy to increasedecomposition routines.

As shown in FIGS. 1 and 2, the mixing system 16 may include a firstmixing device 20, a second mixing device 22 and a baffle plate 24. Thefirst and second mixing devices 20, 22 and the baffle plate 24 may bespaced apart from each other and disposed downstream of the injector 19.The first mixing device 20 may be disposed in a first portion 26 of theexhaust pipe 12. The second mixing device 22 and the baffle plate 24 maybe disposed in a second portion 28 of the exhaust pipe 12 disposeddownstream of the first portion 26. In some configurations, the secondportion 28 may be a barrel containing the aftertreatment device 17(e.g., an SCR catalyst). The first portion 26 may have a smallerdiameter than the second portion 28. More generally, first mixing device20 may include an inlet 29 having a smaller cross-sectional area than aninlet 31 of the second mixing device 22. First mixing device 20 includesa longitudinal centerline 30 that is offset from a longitudinalcenterline 32 of the second mixing device 22. The offset between thecenterlines 30, 32 advantageously increases the travel length of thereductant particles. Centerline 30 may extend parallel to centerline 32or at an angle thereto, as depicted in FIG. 2. A transition cone 27 mayfluidly connect the first and second portions 26, 28. The aftertreatmentdevice 17 may be disposed in the second portion 28 downstream of thesecond mixing device 22 and the baffle plate 24. It will be appreciatedthat one or more portions of the exhaust pipe 12, such as one or both ofthe first and second portions 26, 28, as well as first and second mixingdevices 20, 22, could include a circular, oval or polygonalcross-sectional shape or any other cross-sectional shape.

As shown in FIGS. 3-5, the first mixing device 20 may be an auger havinga plurality of generally helical blades 34 supported on a central shaft36. Radially outer edges 37 of the blades 34 may fixedly engage an innerdiametrical surface 40 (FIG. 2) of the first portion 26 of the exhaustpipe 12. The blades 34 may define a plurality of generally helical flowpaths through the first mixing device 20. In the configuration shown inthe figures, the first mixing device 20 includes four blades 34 thatextend 180 degrees around the central shaft 36 and define four differenthelical flow paths. In the configuration shown in the figures, all ofthe blades 34 extend in the same rotational direction around the centralshaft 36. Each of the blades 34 may include a plurality of apertures 38that allow some fluid communication between the flow paths. Reductantinjected by the injector 19 is atomized as it flows through the firstmixing device 20. Further, the blades 34 of the first mixing device 20induce turbulence in the flow of exhaust gas and reductant, whichfacilitates mixing of the reductant and the exhaust gas. The helicalshapes of the flow paths through the first mixing device 20 increase theamount of time that the reductant is resident in the exhaust gas,thereby increasing evaporation of the reductant without increasing anaxial distance that the reductant travels. The apertures 38 in theblades 34 reduce backpressure created by the first mixing device 20 anddecrease the surface area of the blades 34, thereby reducing theproduction of reductant deposits on the blades 34.

The central shaft 36 may be tapered such that the diameter of thecentral shaft 36 decreases as the shaft 36 extends axially from anupstream end 41 of the shaft 36 to a downstream end 42 of the shaft 36.This tapered shape of the shaft 36 reduces flow separation as theexhaust gas and reductant flow through the first mixing device 20.Upstream ends 43 of all of the blades 34 may all be disposed at the sameaxial position relative to the upstream end 41 of the shaft 36, anddownstream ends 45 of all of the blades 34 may all be disposed at thesame axial position relative to the downstream end 42 of the shaft 36(i.e., all of the blades 34 may have the same axial length and may belocated at the same axial position along the longitudinal axis of theshaft 36).

As shown in FIGS. 6-8, the second mixing device 22 may be an augerhaving one or more generally helical blades 44 attached to and extendingaround a central shaft 46. The second mixing device 22 may include asingle blade 44 that may extend about 360 degrees (or between about 180and 720 degrees, for example) around the shaft 46. A radially outer edge47 of the blade 44 may fixedly engage an inner diametrical surface 49(FIG. 2) of the second portion 28 of the exhaust pipe 12. The helicalshape of the flow path defined by the blade 44 increases the amount oftime that the reductant is resident in the exhaust gas, therebyincreasing evaporation of the reductant without increasing an axialdistance that the reductant travels. The pitch angle of the blade 44 ofthe second mixing device 22 can be different than the pitch angles ofthe blades 34 of the first mixing device 20. In some configurations, thepitch angles of the blades 34 may be greater than the pitch angle of theblade 44. In other configurations, the pitch angle of the blade 44 maybe greater than the pitch angles of the blades 34. The orientation,right hand or left hand, direction of the helical shape of blades 34 maybe the same or different than the orientation of the helically-shapedblade 44. As such, exhaust gas may be urged to rotate in a firstdirection by blades 34 and either continue to be urged in the samedirection of rotation by blade 44 or in the opposite direction ofrotation by a version of blade 44 having the opposite orientation of thehelical shape.

It should also be appreciated that the scope of the present disclosureincludes possibly swapping the positions of first mixing device 20 andsecond mixing device 22 such that second mixing device 22 may bepositioned upstream of first mixing device 20. The first mixing device20 includes an inlet with a smaller cross-sectional area than the inletof second mixing device 22. The transition between one device to thenext may be accomplished through gradual means of a tapered expansion orreduction. In the alternate arrangement described, the upstream mixingdevice defines a single flow path while the downstream mixing deviceincludes more than one gas flow path.

Returning to FIGS. 6-8, blade 44 can include a plurality of apertures 48that reduce backpressure created by the second mixing device 22 anddecrease the surface area of the blade 44, thereby reducing theproduction of reductant deposits on the blade 44. In someconfigurations, the blade 44 can include flaps, dimples, ridges and/orother surface features instead of or in addition to the apertures 48 todirect flow through the apertures 48 and/or influence macroscopic flowthrough the second mixing device 22.

The shaft 46 may include an aperture 50 extending axially therethrough.The aperture 50 reduces backpressure created by the second mixing device22 and may eliminate a flow velocity “dead zone” at the center of theaftertreatment device 17. An upstream end 52 of the shaft 46 can beangled relative to a longitudinal axis of the shaft 46 to reducestagnation at the leading edge of the aperture 50. In someconfigurations, the angle of the upstream end 52 can be approximatelyequal to the pitch angle of the blade 44. In some instances the shaft 46and/or the aperture 50 may be tapered such that a cross-sectional areaof the aperture 50 decreases as the shaft 46 extends from an upstreamposition to a downstream position in similar fashion to central shaft36.

As shown in FIG. 9, the baffle plate 24 may include a plurality of firstapertures 54, a plurality of second apertures 56 and a plurality ofthird apertures 58. A radially outer periphery 60 of the baffle plate 24may fixedly engage the inner diametrical surface 49 (FIG. 2) of thesecond portion 28 of the exhaust pipe 12. The first apertures 54 may bedisposed proximate a periphery 60 of the baffle plate 24 and are eachsmaller than the second and third apertures 56, 58. The second apertures56 may be disposed radially between the first apertures 54 and the thirdapertures 58. The second apertures 56 may be smaller than the thirdapertures 58. The third apertures 58 may be arranged proximate a centerof the baffle plate 24. Each of the third apertures 58 may besubstantially larger than each of the first and second apertures 54, 56.In some configurations, a fourth aperture 62 may be centered on thelongitudinal axis of the baffle plate 24. The configuration of theapertures 54, 56, 58, 62 described above and shown in the figures canredistribute the flow toward a laminar condition prior to the flowentering the aftertreatment device 17. Furthermore, the configuration ofthe apertures 54, 56, 58, 62 can separate high-velocity flow near thewall of the second portion 28 of the exhaust pipe 12. In someconfigurations, the baffle plate 24 can restrict the flow through thesecond portion 28 of the exhaust pipe 12 by about 50% or more.

FIG. 10 depicts an alternate mixing system 16′. Mixing system 16′ issubstantially similar to mixing system 16. As such, similar elementswill be identified with like reference numerals including a primesuffix. A detailed description of the substantially similar featureswill not be provided in this section of the description. It should beappreciated, however, that the previously provided specification appliesto mixing system 16′, as appropriate.

Mixing system 16′ includes a first mixing device 20′, a second mixingdevice 22′, and a baffle plate 24′. A transition cone 27′ and theremaining elements downstream from this component may be identical tothe elements depicted in FIG. 2.

Exhaust pipe 12′ differs from exhaust pipe 12 in that exhaust pipe 12′includes an “S-shaped” bend 70 interconnecting a supply portion 72 ofthe exhaust pipe 12′ with a first portion 26′ of the exhaust pipe 12′.First mixing device 20′ is disposed within first portion 26′ andincludes a longitudinal centerline 30′ extending parallel tolongitudinal centerline 32′ of second mixing device 22′. Injector 19′ isconfigured to inject a reductant along an injection axis 74. Injectionaxis 74 may, but need not, extend parallel to longitudinal centerline30′ of first mixing device 20′. The position and orientation of firstmixing device 20′ addresses the asymmetric flow caused by S-bend 70. Thefirst mixing device 20′ functions to redistribute flow into multipleflow paths. In particular, first mixing device 20′ separates high andlow velocity flows to adjust the maldistribution of flow created byS-bend 70 prior to the exhaust flow engaging second mixing device 22′.The asymmetric exhaust gas flow upstream of first mixing device 20′ incombination with a varied distribution of droplet size injected byinjector 19′ results in larger reductant droplets entering one portionof first mixing device 20′ and smaller droplets entering a differentportion of first mixing device 20′. The subdivision of flow based ondroplet size results in a more efficient decomposition of the reductantwithin the individual flow paths.

It may be beneficial to rotationally orient the second mixing device 22′relative to the position of an outlet 80 of first mixing device 20′. Inparticular, it may be desirable to position an upstream portion 82 ofhelical blade 44 such that upstream portion 82 covers at least 75% ofthe cross-sectional area of outlet 80 of first mixing device 20′. In oneinstance, this goal may be accomplished by positioning a leading edge 84of helical blade 44 at a rotational position similar to the one depictedin FIG. 11. By rotationally positioning leading edge 84 and upstreamportion 82 in this manner, sufficient mixing and interaction with secondmixing device 22′ is assured.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A mixing system for an exhaust aftertreatmentsystem, the mixing system comprising: a first mixing device including aplurality of first auger blades attached to a central shaft and defininga plurality of flow paths through the first mixing device, each of thefirst auger blades being axially aligned with each other and angularlyspaced apart from each other, the first mixing device further includinga longitudinal centerline and an inlet having a first cross-sectionalarea; and a second mixing device separate and distinct from the firstmixing device and disposed downstream of the first mixing device, thesecond mixing device including a longitudinal centerline, an inlethaving a second cross-sectional area greater than the firstcross-sectional area and a second auger blade, the plurality of flowpaths created by the first mixing device recombining into a single flowpath between the first and second mixing devices, the longitudinalcenterline of the first mixing device being offset from the longitudinalcenterline of the second mixing device, wherein the first mixing deviceis disposed within a first portion of an exhaust pipe and the secondmixing device is disposed in a second portion of the exhaust pipe, thesecond portion having a larger diameter than the first portion.
 2. Themixing system of claim 1, further comprising a baffle plate separate anddistinct from the second mixing device and disposed downstream of thesecond mixing device.
 3. The mixing system of claim 1, wherein thecentral shaft of the first mixing device is tapered.
 4. The mixingsystem of claim 1, wherein the central shaft of the second mixing deviceis tapered.
 5. The mixing system of claim 1, wherein the second augerblade includes an upstream portion adjacent to a leading edge of thesecond auger blade, the leading edge being positioned to provide atleast 75% coverage of an exit of the first mixing device.
 6. The mixingsystem of claim 1, wherein the second mixing device includes a centralshaft about which the second auger blade extends, the central shafthaving an aperture extending axially therethrough.
 7. The mixing systemof claim 1, wherein each of the first auger blades includes a pluralityof apertures.
 8. The mixing system of claim 1, wherein each of the firstauger blades extends 180 degrees around the central shaft.
 9. The mixingsystem of claim 8, wherein the first auger blades extend in the samerotational direction around the central shaft.
 10. The mixing system ofclaim 1, wherein the second auger blade include a plurality ofapertures.
 11. The mixing system of claim 1, wherein the second augerblade extends 360 degrees around a second central shaft.
 12. The mixingsystem of claim 1, wherein the second auger blade extends between 180degrees and 720 degrees around a second central shaft.
 13. The mixingsystem of claim 1, wherein the second mixing device includes only asingle auger blade.
 14. An exhaust aftertreatment system comprising themixing system of claim 1, and further comprising: a reductant injectordisposed upstream of the first mixing device; and a catalyst disposeddownstream of the baffle plate.
 15. A mixing system for an exhaustaftertreatment system, the mixing system comprising: a first mixingdevice including a plurality of first auger blades attached to a centralshaft and defining a plurality of flow paths through the first mixingdevice, each of the first auger blades being axially aligned with eachother and angularly spaced apart from each other, the first mixingdevice further including a longitudinal centerline and an inlet having afirst cross-sectional area; a second mixing device separate and distinctfrom the first mixing device and disposed downstream of the first mixingdevice, the second mixing device including a longitudinal centerline, aninlet having a second cross-sectional area greater than the firstcross-sectional area and a second auger blade, the plurality of flowpaths created by the first mixing device recombining into a single flowpath between the first and second mixing devices, the longitudinalcenterline of the first mixing device being offset from the longitudinalcenterline of the second mixing device; and a baffle plate separate anddistinct from the second mixing device and disposed downstream of thesecond mixing device, wherein the baffle plate includes a plurality offirst apertures, a plurality of second apertures and a plurality ofthird apertures, the first apertures are disposed proximate a peripheryof the baffle plate and are each smaller than the second and thirdapertures, the second apertures are disposed radially between the firstapertures and the third apertures and are each smaller than the thirdapertures, the third apertures are arranged proximate a center of thebaffle plate.
 16. The mixing system of claim 15, wherein the firstmixing device is disposed within a first portion of the exhaust pipe,and wherein the second mixing device and the baffle plate are disposedin a second portion of the exhaust pipe, the second portion having alarger diameter than the first portion.
 17. The mixing system of claim16, wherein a longitudinal centerline of the first portion is offsetfrom a longitudinal centerline of the second portion.
 18. A mixingsystem for an exhaust aftertreatment system, the mixing system disposedwithin an exhaust pipe and comprising: a first mixing device including aplurality of first auger blades defining a plurality of flow pathsthrough the first mixing device, the first mixing device furtherincluding a longitudinal centerline and an inlet having a firstcross-sectional area; a second mixing device separate and distinct fromthe first mixing device and disposed downstream of the first mixingdevice, the second mixing device including a longitudinal centerline, aninlet having a second cross-sectional area greater than the firstcross-sectional area and a second auger blade, the plurality of flowpaths created by the first mixing device recombining into a single flowpath between the first and second mixing devices; and a baffle plateseparate and distinct from the second mixing device and disposeddownstream of the second mixing device, the longitudinal centerline ofthe first mixing device being offset from the longitudinal centerline ofthe second mixing device, wherein the first mixing device is disposedwithin a first portion of the exhaust pipe, and wherein the secondmixing device and the baffle plate are disposed in a second portion ofthe exhaust pipe, the second portion having a larger diameter than thefirst portion.
 19. The mixing system of claim 18, wherein the firstmixing device includes a tapered central shaft about which the firstauger blades extend.
 20. The mixing system of claim 19, wherein thesecond mixing device includes a central shaft about which the secondauger blade extends, the central shaft having an aperture extendingaxially therethrough.
 21. The mixing system of claim 19, wherein each ofthe first auger blades includes a plurality of apertures.
 22. The mixingsystem of claim 21, wherein each of the first auger blades extends 180degrees around a central shaft.
 23. The mixing system of claim 22,wherein the first auger blades extend in the same rotational directionaround the central shaft.
 24. The mixing system of claim 21, wherein thesecond auger blade include a plurality of apertures.
 25. The mixingsystem of claim 24, wherein the second auger blade extends 360 degreesaround a central shaft.
 26. The mixing system of claim 25, wherein thesecond mixing device includes only a single auger blade.
 27. The mixingsystem of claim 18, wherein the second auger blade extends between 180degrees and 720 degrees around a second central shaft.
 28. The mixingsystem of claim 18, wherein a longitudinal centerline of the firstportion is offset from a longitudinal centerline of the second portion.29. An exhaust aftertreatment system comprising the mixing system ofclaim 18, and further comprising: a reductant injector disposed upstreamof the first mixing device; and a catalyst disposed downstream of thebaffle plate.
 30. A mixing system for an exhaust aftertreatment system,the mixing system disposed within an exhaust pipe and comprising: afirst mixing device including a plurality of first auger blades defininga plurality of flow paths through the first mixing device, the firstmixing device further including a longitudinal centerline and an inlethaving a first cross-sectional area; a second mixing device separate anddistinct from the first mixing device and disposed downstream of thefirst mixing device, the second mixing device including a longitudinalcenterline, an inlet having a second cross-sectional area greater thanthe first cross-sectional area and a second auger blade, the pluralityof flow paths created by the first mixing device recombining into asingle flow path between the first and second mixing devices; and abaffle plate separate and distinct from the second mixing device anddisposed downstream of the second mixing device, the longitudinalcenterline of the first mixing device being offset from the longitudinalcenterline of the second mixing device, wherein the baffle plateincludes a plurality of first apertures, a plurality of second aperturesand a plurality of third apertures, the first apertures are disposedproximate a periphery of the baffle plate and are each smaller than thesecond and third apertures, the second apertures are disposed radiallybetween the first apertures and the third apertures and are each smallerthan the third apertures, the third apertures are arranged proximate acenter of the baffle plate.
 31. A mixing system for an exhaustaftertreatment system, the mixing system comprising: a first mixingdevice including a plurality of first auger blades attached to a centralshaft and defining a plurality of flow paths through the first mixingdevice, a flow path longitudinal centerline, and an inlet having a firstcross-sectional area; and a second mixing device separate and distinctfrom the first mixing device and disposed downstream of the first mixingdevice, the second mixing device including a flow path longitudinalcenterline, an inlet having a second cross-sectional area greater thanthe first cross-sectional area and a second auger blade, the flow pathlongitudinal centerline of the first mixing device being offset from theflow path longitudinal centerline of the second mixing device, whereinthe longitudinal centerlines are parallel, wherein the first mixingdevice is disposed within a first portion of an exhaust pipe and thesecond mixing device is disposed in a second portion of the exhaustpipe, the second portion having a larger diameter than the firstportion.
 32. The mixing system of claim 31, further comprising a baffleplate separate and distinct from the second mixing device and disposeddownstream of the second mixing device.
 33. The mixing system of claim32, wherein the first mixing device is disposed within a first portionof the exhaust pipe, and wherein the second mixing device and the baffleplate are disposed in a second portion of the exhaust pipe, the secondportion having a larger diameter than the first portion.
 34. The mixingsystem of claim 33, wherein a longitudinal centerline of the firstportion is offset from a longitudinal centerline of the second portion.